package .bin/ scripts as proper nix packages, delete .bin/

Packaged 14 scripts from .bin/ into packages/ with proper dependency
declarations (writers.writeDashBin/writeBashBin/writePython3Bin):
- 256color → two56color (terminal color chart)
- avesta.sed → avesta (Avestan transliteration)
- bvg.sh → bvg (Berlin transit disruptions)
- unicode → charinfo (Unicode character info)
- chunk-pdf → chunk-pdf (split PDFs by page count)
- csv2json → csv2json (CSV to JSON converter)
- fix-sd.sh → fix-sd (exFAT SD card recovery, improved output handling)
- json2csv → json2csv (JSON to CSV converter)
- mp3player-write → mp3player-write (audio conversion for MP3 players)
- mushakkil.sh → mushakkil (Arabic diacritization)
- nix-haddock-index → nix-haddock-index (GHC Haddock index generator)
- pdf-ocr.sh → pdf-ocr (OCR PDFs via tesseract)
- prospekte.sh → prospekte (German supermarket flyer browser)
- readme → readme (GitHub README as man page)

All added to overlay and packages output. .bin/ directory removed.

packages/avesta.nix

@@ -0,0 +1,65 @@
+# Transliterate Latin-script Avestan to Avestan Unicode script
+{
+  writers,
+  gnused,
+}:
+let
+  sedScript = builtins.toFile "avesta.sed" ''
+    s/ā̊/𐬃/g
+    s/t̰/𐬝/g
+    s/ṣ̌/𐬴/g
+    s/š́/𐬳/g
+    s/ą̄/𐬅/g
+    s/ŋᵛ/𐬤/g
+    s/ə̄/𐬇/g
+    s/ŋ́/𐬣/g
+    s/x́/𐬒/g
+    s/xᵛ/𐬓/g
+    s/a/𐬀/g
+    s/ā/𐬁/g
+    s/å/𐬂/g
+    s/ą/𐬄/g
+    s/ə/𐬆/g
+    s/e/𐬈/g
+    s/ē/𐬉/g
+    s/o/𐬊/g
+    s/ō/𐬋/g
+    s/i/𐬌/g
+    s/ī/𐬍/g
+    s/u/𐬎/g
+    s/ū/𐬏/g
+    s/k/𐬐/g
+    s/x/𐬑/g
+    s/g/𐬔/g
+    s/ġ/𐬕/g
+    s/γ/𐬖/g
+    s/c/𐬗/g
+    s/j/𐬘/g
+    s/t/𐬙/g
+    s/θ/𐬚/g
+    s/d/𐬛/g
+    s/δ/𐬜/g
+    s/p/𐬞/g
+    s/f/𐬟/g
+    s/b/𐬠/g
+    s/β/𐬡/g
+    s/ŋ/𐬢/g
+    s/n/𐬥/g
+    s/ń/𐬦/g
+    s/ṇ/𐬧/g
+    s/m/𐬨/g
+    s/m̨/𐬩/g
+    s/ẏ/𐬫/g
+    s/y/𐬪/g
+    s/v/𐬬/g
+    s/r/𐬭/g
+    s/s/𐬯/g
+    s/z/𐬰/g
+    s/š/𐬱/g
+    s/ž/𐬲/g
+    s/h/𐬵/g
+  '';
+in
+writers.writeDashBin "avesta" ''
+  exec ${gnused}/bin/sed -f ${sedScript} "$@"
+''